1. Field of the Invention
The invention resides in the field of electrically controlled actuators and more particularly relates to devices composed of a plurality of electrically conductive dissimilar materials having junctions which, upon the passage of electrical current, will be rendered hot or cold depending upon the direction of current flow.
2. Description of the Prior Art
Thermoelectric actuators wherein an electric current is passed through a composite of layered dissimilar materials are known in the prior art. In particular, U.S. Pat. No. 6,161,382 issued to the present inventor discloses a three-layered metallic or semiconductor strip which reacts to the passage of an electrical current across it by generating a relative hot-cold temperature gradient at each material interface as a result of the Peltier effect. The gradient within the composite results in uneven expansion or contraction of the device, depending upon the direction of current flow, causing the device to bend in one direction or the other which bending may be used to do work as a mechanical actuator.
The theoretical background of the Peltier effect and material expansion is treated extensively in the above referenced patent. In summary, electron flow at the junction of two dissimilar conductive materials will result either in a cooling or heating of the junction depending upon the identity of the materials and the direction of current flow. In the prior art, this effect was used to form a multilayered actuator whose size was limited to the area of the sheets forming the composite.
The invention disclosed herein, while utilizing the same scientific principle, presents an actuator which can be of almost any size and can additionally be varied or controlled at selected positions along its width to achieve complex shapes or profiles. The multijunction thermoelectric actuator of this invention is composed of a series of serially connected, alternating strips of electrically conducting dissimilar materials alternatively joined or having junctions at their upper and lower surfaces. The completed device comprises a sheet of any desired, or practical, dimension of length or width. The total length is the length of the individual strips and the total width is the sum of the widths of the individual strips. Electrical power applied across the width, i.e., from strip to strip will produce a heating effect on one surface and a cooling effect on the opposite surface originating at each connecting junction. The process is reversible such that when the direction of current flow is reversed, the heating and cooling of the surfaces are reversed.
Ideally the strips alternate as to material composition although as long as alternating strips are electrically equivalent with respect to the Peltier effect, they do not have to be identical. P and N type semiconductors are suggested as suitable materials, and the invention will be described in the context of this example.
The unequal expansion and contraction resulting from the temperature gradient between the upper and lower surfaces results in the composite bending toward the heated side. This bending can be used to do work as an actuator, or to modify a surface, for example, for optical transmissions or reflections or to present a varying curved surface for other mechanical purposes, such as an airfoil.
In the most basic embodiment of the invention, the strips are joined by connecting conductors. They can also be constructed so as to overlap to form their own junctions directly without resort to intermediate connectors.
Additionally, as the invention can comprise many serially connected sets of alternating strips, power can be supplied at various points across the composite rather than only at each outer edge. A programmable power supply having a plurality of output points can then be used to alter the shape of the overall sheet in a complex manner rather than a simple bend toward one side or the other.